In conventional CATV systems, certain premium channels may be offered to authorized subscribers for an additional monthly fee or on a selective basis through the implementation of so-called impulse pay-per-view (IPPV) technology. Various techniques have been developed in order to ensure that events carried on these premium channels are available only to those subscribers authorized to receive the events. One technique developed for premium channel control is an interdiction system in which an interfering signal is introduced into the television signal at a subscriber's location. Such an interdiction system is described in U.S. Pat. No. 4,912,760. A typical interdiction system includes a pole-mounted unit located outside or "off" the subscriber's premises and which is designed to serve at least one and up to four or more subscribers. The unit contains at least one microprocessor controlled oscillator and switch control electronics to secure several premium television channels. Control is accomplished by injecting an interfering or jamming signal into unauthorized channels from the pole-mounted unit. To improve efficiency and to save costs, one oscillator may be used to jam several premium television channels. This technique reduces the amount of hardware required and maximizes system flexibility. The oscillator output jamming signal frequency is periodically moved from channel to channel. Consequently, the oscillator is frequency agile and hops from jamming one premium channel frequency to the next.
One advantage of interdiction systems is a ready access by a cable operator to the equipment since entry into a subscriber's house is not necessary. Further, since the interdiction unit is located outside a subscriber's premises, pirates have reduced opportunity to examine and effect changes to system circuitry in attempts to defeat the premium channel controls implemented by the system operator. Finally, costs may be reduced since a single interdiction unit may serve a plurality of subscribers.
However, in most, if not all CATV systems, situations arise when it is desirable or necessary to provide a return or reverse path from a particular subscriber to a headend. A number of special services may be realized over a cable television distribution plant if a reverse path is provided. Such services include remote utility meter reading, fire and burglar alarm, energy management, home shopping, subscriber polling or voting, educational and pay-per-view television services. However, in the 1970's and 1980's the preponderance, if not most, of subscriber service providing equipment was physically located on the subscriber's premises. Consequently, little attention was paid to a problem of providing reverse path transmission in an off-premises subscriber equipment environment, such as exists in a CATV interdiction system.
One situation in which some type of reverse path is needed for interdiction systems is in pay-per-view and impulse pay-per-view technology. This technology allows a subscriber to choose a presentation such as a first-run movie or a prize fight on a selective basis when the subscriber desires to view such an event. In many CATV systems, a pay-per-view event is ordered through the use of telephone calls from subscribers to the cable operator who then authorizes the subscriber to receive the event, usually by sending an authorization signal which activates a descrambler in a set top converter or terminal used by the subscriber. Since time is required to allow the cable operator to program the set top converters to allow viewing of the event, the event must be ordered well in advance of the time that they are broadcast in order to ensure reception. Other systems utilize the set top converter as a subscriber interface. The set top converter is tuned by the subscriber to select the premium channel, then the subscriber enters his or her authorization number. The set top converter then activates its descrambler to allow the broadcast on the selected premium channel to be received. Information regarding the purchase is stored in the set top converter. The converter interface is provided with telephone connection circuits which place calls to the cable operator (or reverse path RF transmitters which transmit to the cable operator) and transfer data as to the pay per view events which were selected. Although such set top converters interfaces provide IPPV capability, they are not suitable when, instead of set top converters, off premises equipment deliver broad band signals to the subscribers. The off premises equipment has no knowledge of which channel the subscriber is watching and cannot relay billing information to the cable operator as to the events which have been selected.
Commonly assigned, copending application Ser. No. 612,933, entitled "CATV System Enabling Access to Premium (Pay-Per-View) Program Events By Bar Code Data Entry" filed Nov. 13, 1990, (Attorney Docket No. A-317) discloses a system in which programs of events broadcast on premium channels of a CATV system may be purchased by means of a bar code entry terminal. However, the bar code entry terminal on the subscriber premises is a complex device which must read bar code symbols and be capable of two-way communication with the off-premises equipment. Complex devices on the subscriber premises compromise the cost savings achieved with an interdiction system.